Method and system for aligning natural and synthetic video to speech synthesis

ABSTRACT

According to MPEG-4&#39;s TTS architecture, facial animation can be driven by two streams simultaneously—text, and Facial Animation Parameters. In this architecture, text input is sent to a Text-To-Speech converter at a decoder that drives the mouth shapes of the face. Facial Animation Parameters are sent from an encoder to the face over the communication channel. The present invention includes codes (known as bookmarks) in the text string transmitted to the Text-to-Speech converter, which bookmarks are placed between words as well as inside them. According to the present invention, the bookmarks carry an encoder time stamp. Due to the nature of text-to-speech conversion, the encoder time stamp does not relate to real-world time, and should be interpreted as a counter. In addition, the Facial Animation Parameter stream carries the same encoder time stamp found in the bookmark of the text. The system of the present invention reads the bookmark and provides the encoder time stamp as well as a real-time time stamp to the facial animation system. Finally, the facial animation system associates the correct facial animation parameter with the real-time time stamp using the encoder time stamp of the bookmark as a reference.

BACKGROUND OF THE INVENTION

The present invention relates generally to methods and systems forcoding of images, and more particularly to a method and system forcoding images of facial animation.

According to MPEG-4's TTS architecture, facial animation can be drivenby two streams simultaneously—text, and Facial Animation Parameters(FAPs). In this architecture, text input is sent to a Text-To-Speech(TTS) converter at a decoder that drives the mouth shapes of the face.FAPs are sent from an encoder to the face over the communicationchannel. Currently, the Verification Model (VM) assumes thatsynchronization between the input side and the FAP input stream isobtained by means of timing injected at the transmitter side. However,the transmitter does not know the timing of the decoder TTS. Hence, theencoder cannot specify the alignment between synthesized words and thefacial animation. Furthermore, timing varies between different TTSsystems. Thus, there currently is no method of aligning facial mimics(e.g., smiles, and expressions) with speech.

The present invention is therefore directed to the problem of developinga system and method for coding images for facial animation that enablesalignment of facial mimics with speech generated at the decoder.

SUMMARY OF THE INVENTION

The present invention solves this problem by including codes (known asbookmarks) in the text string transmitted to the Text-to-Speech (TTS)converter, which bookmarks can be placed between words as well as insidethem. According to the present invention, the bookmarks carry an encodertime stamp (ETS). Due to the nature of text-to-speech conversion, theencoder time stamp does not relate to real-world time, and should beinterpreted as a counter. In addition, according to the presentinvention, the Facial Animation Parameter (FAP) stream carries the sameencoder time stamp found in the bookmark of the text. The system of thepresent invention reads the bookmark and provides the encoder time stampas well as a real-time time stamp (RTS) derived from the timing of itsTTS converter to the facial animation system. Finally, the facialanimation system associates the correct facial animation parameter withthe real-time time stamp using the encoder time stamp of the bookmark asa reference. In order to prevent conflicts between the encoder timestamps and the real-time time stamps, the encoder time stamps have to bechosen such that a wide range of decoders can operate.

Therefore, in accordance with the present invention, a method forencoding a facial animation including at least one facial mimic andspeech in the form of a text stream, comprises the steps of assigning apredetermined code to the at least one facial mimic, and placing thepredetermined code within the text stream, wherein said code indicates apresence of a particular facial mimic. The predetermined code is aunique escape sequence that does not interfere with the normal operationof a text-to-speech synthesizer.

One possible embodiment of this method uses the predetermined code as apointer to a stream of facial mimics thereby indicating asynchronization relationship between the text stream and the facialmimic stream.

One possible implementation of the predetermined code is an escapesequence, followed by a plurality of bits, which define one of a set offacial mimics. In this case, the predetermined code can be placed inbetween words in the text stream, or in between letters in the textstream.

Another method according to the present invention for encoding a facialanimation includes the steps of creating a text stream, creating afacial mimic stream, inserting a plurality of pointers in the textstream pointing to a corresponding plurality of facial mimics in thefacial mimic stream, wherein said plurality of pointers establish asynchronization relationship with said text and said facial mimics.

According to the present invention, a method for decoding a facialanimation including speech and at least one facial mimic includes thesteps of monitoring a text stream for a set of predetermined codescorresponding to a set of facial mimics, and sending a signal to avisual decoder to start a particular facial mimic upon detecting thepresence of one of the set of predetermined codes.

According to the present invention, an apparatus for decoding an encodedanimation includes a demultiplexer receiving the encoded animation,outputting a text stream and a facial animation parameter stream,wherein said text stream includes a plurality of codes indicating asynchronization relationship with a plurality of mimics in the facialanimation parameter stream and the text in the text stream, a text tospeech converter coupled to the demultiplexer, converting the textstream to speech, outputting a plurality of phonemes, and a plurality ofreal-time time stamps and the plurality of codes in a one-to-onecorrespondence, whereby the plurality of real-time time stamps and theplurality of codes indicate a synchronization relationship between theplurality of mimics and the plurality of phonemes, and a phoneme tovideo converter being coupled to the text to speech converter,synchronizing a plurality of facial mimics with the plurality ofphonemes based on the plurality of real-time time stamps and theplurality of codes.

In the above apparatus, it is particularly advantageous if the phonemeto video converter includes a facial animator creating a wireframe imagebased on the synchronized plurality of phonemes and the plurality offacial mimics, and a visual decoder being coupled to the demultiplexerand the facial animator, and rendering the video image based on thewireframe image.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a environment in which the present invention will beapplied.

FIG. 2 depicts the architecture of an MPEG-4 decoder usingtext-to-speech conversion.

DETAILED DESCRIPTION

According to the present invention, the synchronization of the decodersystem can be achieved by using local synchronization by means of eventbuffers at the input of FA/AP/MP and the audio decoder. Alternatively, aglobal synchronization control can be implemented.

A maximum drift of 80 msec between the encoder time stamp (ETS) in thetext and the ETS in the Facial Animation Parameter (FAP) stream istolerable.

One embodiment for the syntax of the bookmarks when placed in the textstream consists of an escape signal followed by the bookmark content,e.g., \!M{bookmark content}. The bookmark content carries a 16-bitinteger time stamp ETS and additional information. The same ETS is addedto the corresponding FAP stream to enable synchronization. The class ofFacial Animation Parameters is extended to carry the optional ETS.

If an absolute clock reference (PCR) is provided, a drift compensationscheme can be implemented. Please note, there is no master slave notionbetween the FAP stream and the text. This is because the decoder mightdecide to vary the speed of the text as well as a variation of facialanimation might become necessary, if an avatar reacts to visual eventshappening in its environment.

For example, if Avatar 1 is talking to the user. A new Avatar enters theroom. A natural reaction of avatar I is to look at avatar 2, smile andwhile doing so, slowing down the speed of the spoken text.

Autonomous Animation Driven Mostly by Text

In the case of facial animation driven by text, the additional animationof the face is mostly restricted to events that do not have to beanimated at a rate of 30 frames per second. Especially high-level actionunits like smile should be defined at a much lower rate. Furthermore,the decoder can do the interpolation between different action unitswithout tight control from the receiver.

The present invention includes action units to be animated and theirintensity in the additional information of the bookmarks. The decoder isrequired to interpolate between the action units and their intensitiesbetween consecutive bookmarks.

This provides the advantages of authoring animations using simple tools,such as text editors, and significant savings in bandwidth.

FIG. 1 depicts the environment in which the present invention is to beused. The animation is created and coded in the encoder section 1. Theencoded animation is then sent through a communication channel (orstorage) to a remote destination. At the remote destination, theanimation is recreated by the decoder 2. At this stage, the decoder 2must synchronize the facial animations with the speech of the avatarusing only information encoded with the original animation.

FIG. 2 depicts the MPEG-4 architecture of the decoder, which has beenmodified to operate according to the present invention. The signal fromthe encoder 1 (not shown) enters the Demultiplexer (DMUX) 3 via thetransmission channel (or storage, which can also be modeled as achannel). The DMUX 3 separates outs the text and the video data, as wellas the control and auxiliary information. The FAP stream, which includesthe Encoder Time Stamp (ETS), is also output by the DMUX 3 directly tothe FA/AP/MP 4, which is coupled to the Text-to-Speech Converter (TTS)5, a Phoneme FAP converter 6, a compositor 7 and a visual decoder 8. ALip Shape Analyzer 9 is coupled to the visual decoder 8 and the TTS 5.User input enters via the compositor 7 and is output to the TTS 5 andthe FA/AP/MP 4. These events include start, stop, etc.

The TTS 4 reads the bookmarks, and outputs the phonemes along with theETS as well as with a Real-time Time Stamp (RTS) to the Phoneme FAPConverter 6. The phonemes are used to put the vertices of the wireframein the correct places. At this point the image is not rendered.

This data is then output to the visual decoder 8, which renders theimage, and outputs the image in video form to the compositor 7. It is inthis stage that the FAPs are aligned with the phonemes by synchronizingthe phonemes with the same ETS/RTS combination with the correspondingFAP with the matching ETS.

The text input to the MPEG-4 hybrid text-to-speech (TTS) converter 5 isoutput as coded speech to an audio decoder 10. In this system, the audiodecoder 10 outputs speech to the compositor 7, which acts as theinterface to the video display (not shown) and the speakers (not shown),as well as to the user.

On the video side, video data output by the DMUX 3 is passed to thevisual decoder 8, which creates the composite video signal based on thevideo data and the output from the FA/AP/MP 4.

There are two different embodiments of the present invention. In a firstembodiment, the ETS placed in the text stream includes the facialanimation. That is, the bookmark (escape sequence) is followed by a 16bit codeword that represents the appropriate facial animation to besynchronized with the speech at this point in the animation.

Alternatively, the ETS placed in the text stream can act as a pointer intime to a particular facial animation in the FAP stream. Specifically,the escape sequence is followed by a 16 bit code that uniquelyidentifies a particular place in the FAP stream.

While the present invention has been described in terms of animationdata, the animation data could be replaced with natural audio or videodata. More specifically, the above description provides a method andsystem for aligning animation data with text-to-speech data. However,the same method and system applies if the text-to-speech data isreplaced with audio or video. In fact, the alignment of the two datastreams is independent of the underlying data, at least with regard tothe TTS stream.

What is claimed is:
 1. A method for encoding a facial animationcomprising the steps of: a) creating a data stream; b) creating a facialmimic stream including a plurality of facial animation parameters; c)inserting a plurality of time stamps in the data stream pointing to saidplurality of facial animation parameters, wherein said plurality of timestamps establishes a synchronization relationship with said data streamand said facial mimic stream; and d) encoding said data stream and saidfacial mimic stream.
 2. The method according to claim 1, furthercomprising inserting said plurality of time stamps in the facial mimicstream.
 3. The method according to claim 1, wherein the data streamcomprises a text stream, and wherein a decoding process converts thetext stream to speech.
 4. The method according to claim 3, furthercomprising the step of placing at least one of the plurality of timestamps in between words in the text stream.
 5. The method according toclaim 3, further comprising the step of placing at least one of theplurality of time stamps in between syllables in the text stream.
 6. Themethod according to claim 3, further comprising the step of placing atleast one of the plurality of time stamps inside words in the textstream.
 7. The method according to claim 1, wherein the data streamcomprises a video stream.
 8. The method according to claim 1, whereinthe data ream comprises an audio stream.
 9. A method for encoding afacial animation including at least one facial mimic and speech in theform of a text stream, comprising the steps of: a) assigning apredetermined code to the at least one facial mimic; b) placing thepredetermined code within the text stream, wherein said predeterminedcode indicates a presence of a particular facial mimic and wherein saidpredetermined code points to a stream of facial mimics, therebyindicating a synchronization relationship between the text stream andthe facial mimic stream; c) encoding said text stream; and d) placingthe predetermined code in between letters in the text stream.
 10. Amethod for encoding a facial animation including at least one facialmimic and speech in the form of a text stream, comprising the steps of:a) assigning a predetermined code to the at least one facial mimic; b)placing the predetermined code within the text stream, wherein saidpredetermined code indicates a presence of a particular facial mimic andwherein said predetermined code points to a stream of facial mimics,thereby indicating a synchronization relationship between the textstream and the facial mimic stream; c) encoding said text stream; and d)placing the predetermined code inside words in the text stream.
 11. Amethod for decoding a facial animation including speech and at least onefacial mimic, comprising the steps of: a) monitoring a text stream for aset of predetermined codes corresponding to a set of facial mimics,wherein the predetermined code points to a stream of facial mimicsestablished during an encoding process of said text stream, therebyindicating a synchronization relationship between the text stream andthe facial mimic stream; b) sending a signal to a visual decoder tostart a particular facial mimic upon detecting the presence of the setof predetermined codes; and c) placing the predetermined code in betweenphonemes in the text stream.
 12. A method for decoding a facialanimation including speech and at least one facial mimic, comprising thesteps of: a) monitoring a text stream for a set of predetermined codescorresponding to a set of facial mimics, wherein the predetermined codepoints to a stream of facial mimics established during an encodingprocess of said text stream, thereby indicating a synchronizationrelationship between the text stream and the facial mimic stream; b)sending a signal to a visual decoder to start a particular facial mimicupon detecting the presence of the set of predetermined codes; and c)placing the predetermined code inside words in the text stream.